Synapses

Question 1

What are graded potentials

Answer 1

1. Graded potentials are activated by synapses from other neurons
2. Above threshold action potentials are generated

Question 2

Describe nerve cell communication

Answer 2

1. Action potentials are generated in presynaptic neurone by graded potentials activated by inputs from other neurones
2. Invade synaptic terminals after propagation
3. Release chemical synaptic transmitter
4. Generate graded potential in postsynaptic neurone
5. Postsynaptic potential can be inhibitory or excitatory
6. Some neurones communicate via electrical junctions

Question 3

What are the two types of synapse

Answer 3

1. Chemical

2. Electrical

Question 4

Describe electrical synapses

Answer 4

1. Electrical synapses- gap junction
2. Formed by connexons in both cell membranes
3. Direct passage of ions and small molecules through channel
4. Permit very rapid faithful transfer of signals
5. Pre- and post-synaptic neurones are directly connected by gap junctions (2 nM)

Question 5

Describe chemical junctions

Answer 5

1. Pre- and post-synaptic neurones are physically separated by synaptic cleft around 30 nm (20-50 nM)
2. Presynaptic neurones release chemical transmitter from their axon terminals
3. Transmitter binds to receptors on post-synaptic neurons
4. No physical connection
5. Chemical released passes to receptors by diffusion across the gap

Question 6

What are axodendritic synapses?

Answer 6

Between the axon of one neurone and the dendrites of another.

Question 7

What are axosomatic synapses?

Answer 7

Between the axon terminals of one and the cell body of another.

Question 8

What are axoaxonal synapses?

Answer 8

1. Between two axons.

2. another synapses can influence transmission by touching the terminal of another synapse

Question 9

Describe the shape of CNS synapses

Answer 9

1. Presynaptic terminals contain vesicles arranged at active zones
2. Postsynaptic membrane is specialised and contains clusters of neurotransmitter receptor and signalling molecules

Question 10

What are the two types of neurotransmitter receptors?

Answer 10

1. Ligand-gated ion channels

2. G-protein coupled receptors.

Question 11

What must a Neurotransmitter be

Answer 11

1. present in axon terminals -presynaptic terminals- along with synthetic material for making it
2. When a stimulus comes released in response to depolarisation (calcium dependent exocytosis)
3. Specific receptors in post membrane mechanism to mediate postsynaptic response
4. Have to show there is a mechanism to get rid of it-

Question 12

Describe how are ligand-gated channels opened?

Answer 12

1. The neurotransmitter binds to the receptor
2. activated resulting in a conformational change such that it forms an open channel
3. channel ionotropic receptor

Question 13

How are G-protein coupled receptors opened?

Answer 13

1. bind to transmitter don’t have ion channel
2. G-protein bind to receptor and then binds to effector protein which sends intracellular messages to a voltage-gated ion channel so that it opens.

Question 14

Where does Ach act?

Answer 14

1. nicotinic (ion channels)

2. muscarinic (G protein coupled) receptors.

Question 15

How is Ach synthesised

Answer 15

1. ACh is synthesised in the presynaptic axon by the enzyme choline acetyltransferase (ChAT)
2. Choline and acetyl CoA combining.

Question 16

How is Ach degraded

Answer 16

1. acetylcholinesterase (AChE) in the cleft

2. Choline and acetic acid.

Question 17

What is Cholinergic transmission

Answer 17

1. A ‘model’ synapse
2. The synapse between motor neurones and skeletal muscle
3. Soma of motor neurone in CNS can be 1 metre from terminals in muscles
4. Junction known as motor endplate
5. Uses Ach as transmitter acting at nicotinic receptors, in same way as CNS synapses.

Question 18

Where does Ach come from

Answer 18

1. Comes from diet and from being reused

2. Not major transmitter in brain

Question 19

Why are neuromuscular junctions used as a model synapse?

Answer 19

They are easy to experiment with and study - they are simple as there is only one input and one output.

Question 20

What are the brains main neurotransmitters

Answer 20

1. Amino acids are the main brain neurotransmitters

Question 21

What are two example of amino acid neurotransmitters

Answer 21

1. Glutamate

2. GABA

Question 22

Describe glutamates role

Answer 22

1. The main excitatory transmitter in the CNS
2. Activates a large number of both ionotropic and metabotropic receptor
3. glutamate generates an excitatory postsynaptic potential (EPSP)

Question 23

Describe GABA roles

Answer 23

1. The main inhibitory transmitter in CNS
2. Activates small family of ionotropic and metabotropic receptors
3. g-aminobutyric acid (GABA) generates an inhibitory postsynaptic potential (IPSP)
4. open channel which is permeable to chloride ions
5. causes hyperpolarisation

Question 24

What is temporal summation

Answer 24

1. adding together potentials that occur at the same synapse but at different times

Question 25

What is spatial summation

Answer 25

1. Adding together potentials that occur at different sites on the nuerone.

Question 26

What are common features of all neurotransmitters

Answer 26

1. presynaptic terminals have vesicles arranged in active zones, with the others dispersed 2. post membrane is specialised and contains clusters of neurotransmitter receptors and signalling molecules

Question 27

Process of release of neurotransmitter by exocytosis

Answer 27

1. vesicles docked at active sites 2. arrival of AP causes VGCC to open 3. calcium ions flow in and allow docked vesicles to fuse with the membrane (some completely fuse and some are recycled by endocytosis)

Question 28

What is needed for action potentials to occur?

Answer 28

Graded potentials to reach above the threshold.

Question 29

What can a drug do

Answer 29

1. increase leakage of neurotransmitter from a vesicle 2. increase transmitter release into cleft 3. inhibit transmitter synthesis 4. block transmitter uptake 5. bind to receptor on post-synaptic membrane to block neurotransmitter (agonist) 6. inhibit or stimulate secondary messenger in post-synaptic cell